1. Field of the Invention
The invention relates to an optical system for nondestructive internal inspection and temperature monitoring of online power generation turbines, including gas turbines with either metal or thermal barrier coated (TBC) turbine blades that are operating with surface temperatures in the range of over 600° C. (1112° F.). More particularly, the present invention relates to an optical system, including an optical tube utilizing a series of mirrors having a spectral reflectivity range from the visible to the long wave infrared, namely 550 nm to 20 μm for gold mirror, and capable of continuous operation at temperatures greater than 932 degrees Fahrenheit (500 degrees Celsius). The same reflective optical system may be used to measure selectively surface temperature of metal turbine blades in the near IR range (approximately 1-2 μm wavelength) and of thermal barrier coated turbine blades in the long IR range (approximately 8-12 μm wavelength).
2. Description of the Prior Art
Infra-red or visible spectrum online camera systems monitor critical internal engine components of a power generation gas turbine, steam turbine, generator or their associated equipment during their operation in a power plant, by combining a high temperature refractive lens optical system with high-speed camera imagery. The optical system design requires selection and combination of lenses and optical material in order to provide the best image quality compatible with the inspected component's emissivity, while surviving within the harsh operating environments of the equipment. It is also preferable, where possible, to use the same optical inspection system components across a broad spectrum of inspection wavelengths for multiple applications in multiple types of internal engine components.
For example, metal turbine blades have high emissivity in the near infra-red 1-2 μm wavelength range. There are suitable refractive lens materials that offer good transmissivity in the near and mid IR 1-5 μm wavelength range that can resist hostile temperature environments of approximately 1000° C. (˜1830° F.) within operating gas turbine blade sections. Thus, camera monitoring systems coupled to those refractive lens optical systems in the near IR range generate good quality images that can be used, among other things, for accurate metal blade surface temperature measurement.
In contrast, gas turbine blades having thermal barrier coatings (TBC) have a high emissivity value in the long IR range around 8-12 μm wavelength. Thus, long IR imaging is preferred for measuring gas turbine TBC blade surface temperature. The 8-12 μm detection band can provide accurate TBC blade surface temperature measurement. However, it is challenging to find suitable long IR refractive lens optical materials that are as robust for optical tubes used in a gas turbine environment as the near IR refractive materials used in near IR optical system optical tubes.
Robust optical tubes are needed in the industry for the continuous online monitoring of internal turbine parts during their entire operating lifecycle. Gas turbines are intended to be operated continuously between scheduled maintenance cycles. The optomechanical components of camera inspection systems cannot be removed from a monitored gas turbine during the latter's operation, until a scheduled maintenance period. Typical maintenance inspection cycles of gas turbines are scheduled every 4000 hours, with typically a major inspection every 8000 hours. It is therefore critical for a continuous online inspection monitoring system to remain operational without disassembly at least 4000 hours before it has a chance to be inspected and serviced.
Thus, a need exists in the art for a high temperature environment inspection system for power system turbines and the like that can withstand continuous operation in temperature environments above 500° C. (932° F.) and desirably up to 1000° C. (1832° F.).
There is another existing need to increase optical transmission efficiency while maintaining and preferably increasing image quality across a multispectral imaging wavelength range without the need to use different optical tubes for different inspection applications.
There is another overall need in the art to increase high temperature inspection system operational service life so that it coincides with scheduled turbine maintenance service periods: desirably for 4000 hours.